1. Field of the Invention
The present invention relates to a photometering apparatus for measuring the brightness of an object to be photographed. More precisely, it relates to a photometer in which a split type light receiving device is used to individually detect the brightness of divided portions of the object in separate areas of a picture plane.
2. Description of Related Art
A conventional split measurement type of photometering apparatus for measuring the brightness of an object to be photographed usually comprises the combination of a condenser lens (i.e., gathering lens) for condensing a bundle of rays reflected from the object, and a split type light receiving device. A diaphragm is usually integrally formed with the condenser lens.
If the condenser lens is made of a single lens, field curvature (i.e., curvature of image) cannot be completely corrected, even by the use of an aspheric surface. Consequently, the spot diameter on the light receiving surface increases as the distance of the beam spot from the optical axis increases.
Accordingly, in a known photometer in which the condenser lens is made of a single lens, it is possible to detect the brightness of a beam spot at the center of the picture plane, but it is impossible to correctly measure the brightness of the beam spot in the peripheral edge portion of the picture plane in which the spot diameter is larger than the width of the split separate areas of the light receiving device.